Just want to stick up for going the Power Commander route - had a PC3 on my 2005 GS (combined with a full BOS system) and it made a HUGE diffrence - yes more power, but also so so so much smoother (especially low down where the increase in 'driveability' made it feel almost like a diffrent bike).
I bought it from the UK importer and fitted it myself. I'm reasonably handy in the Garage but a bit of a numpty in front of a computer (so the nice people I bought it from supplied it with the right map for my bike and setup). The instructions provided and the support over the phone from the supplier were excellent. I have been back to them since with questions about what to do with my new 2010 GSA and have found them extremely knowlwdgeable and helpful.
I have two points to make:
1) unless you are confident / competant enaough to do it all yourself I would suggest you don't buy this sort of kit when you are on holiday / online from someone who won't be there to answer any questions.
2) I've got a feeling (although I can't gaurantee it) that if you have the standard chip remapped it will leave a record to the effect and that they can only be remapped a certain number of times (you probably find that a dealer will check that you have the latest official updates installed when you have the bike serviced).
3) if any of the above starts you worrying about warranty etc - don't do it and don't question people who do!
I know that's three points, but I'm on a roll now.
Going to turn my computer off and hide behind the sofa before it explodes with unhappy relies.
4) if anything is spelt wrong its because I havn't got enough time in my life to work out how to download the sodding spell checker!